Many types of non-volatile storage cells exist in the prior art, including trapped charge devices (such as flash memory), altered resistivity devices (such as phase-change or chalcogenide memory), and many more. Flash memory is relatively fast, but has a short data retention time. Phase-change materials have longer data retention and have access speeds comparable to that of flash, but they are sensitive to temperature extremes during processing. Many memory architectures have also been disclosed in which the storage arrays are constructed in three dimensions (“3D”). Fabricating memory arrays in 3D is challenging because the semiconducting materials used may require high-temperature deposition or anneal steps. Therefore, a need exists for a 3D memory that has the beneficial properties of phase-change memory but that can be constructed at low temperatures.
Diode arrays represent an alternative to CMOS-based phase-change memory and can be constructed as factory-programmed devices, one-time programmable devices, and reprogrammable devices. A diode array is disclosed in U.S. Pat. No. 5,889,694, the disclosure of which is hereby incorporated by reference in its entirety. In that invention, complementary address inputs are utilized. In U.S. Pat. No. 6,586,327 and U.S. patent application Ser. No. 11/707,739 for “Nano-Vacuum-Tubes and Their Application in Storage Devices,” the disclosures of which are hereby incorporated by reference in their entireties, a diode memory is disclosed in which the diodes are constructed with field-emitter devices as the current-rectification elements. In U.S. patent application Ser. No. 11/926,778, the disclosure of which is hereby incorporated by reference in its entirety, a single type of electronic switching device is incorporated to enable the on-chip generation of complementary address pairs and other functionality. Diode memories can be constructed in 3D and at low processing temperatures. When the geometries of a diode array memory become very small, however, the required thickness of the silicon layers that form the diode devices may dictate unacceptably high aspect ratios.